This textbook introduces the current astrophysical observations of black
holes, and discusses the leading techniques to study the strong gravity
region around these objects with electromagnetic radiation. More
importantly, it provides the basic tools for writing an astrophysical
code and testing the Kerr paradigm. Astrophysical black holes are an
ideal laboratory for testing strong gravity. According to general
relativity, the spacetime geometry around these objects should be well
described by the Kerr solution. The electromagnetic radiation emitted by
the gas in the inner part of the accretion disk can probe the metric of
the strong gravity region and test the Kerr black hole hypothesis. With
exercises and examples in each chapter, as well as calculations and
analytical details in the appendix, the book is especially useful to the
beginners or graduate students who are familiar with general relativity
while they do not have any background in astronomy or astrophysics.